(a) Field of the Invention
The present invention relates to a discovery signal that is transmitted in a device to device (D2D) direct communication system, and a method of transmitting/receiving the discovery signal.
(b) Description of the Related Art
Device to device (D2D) direct communication between mobile terminals may be classified into a discovery step of identifying (discovering) an adjacent terminal periodically existing at a periphery for device to device direct communication between terminals, and a step of setting a communication path between identified (discovered) adjacent terminals and of performing direct communication through the set path.
The step of identifying (discovering) an adjacent terminal may be divided into a step of acquiring terminal identifier information and a step of acquiring service related information that a terminal provides. For this purpose, terminals joining in device to device direct communication between mobile terminals (D2D communication) periodically broadcast terminal identifier information thereof or service information. Because an amount of radio resources necessary for broadcasting identifier information of a terminal is relatively small, overhead according to periodic broadcasting through a radio channel is relatively large. However, when at least one service is provided by a terminal, to periodically broadcast all information about the at least one provided service has high overhead and has effectiveness of a lower amount of radio resources, compared with high overhead. Therefore, service information of an existing adjacent terminal is not broadcasted through a radio channel, and terminal identifier information that is generally broadcasted through a radio channel is acquired and is provided through a communication path that is set after a communication path between adjacent terminals is set. Because such a method can negotiate a service after a communication path is set regardless of whether a communication service is actually provided between terminals, an unnecessary direct communication path may be set between adjacent terminals.